The present invention relates to the field of vehicle propulsion systems. More particularly, the invention relates to a hydrostatic vehicle propulsion system consisting of a single, variable fluid displacement pump in conjunction with multiple fluid displacement motors, and a valve system to provide traction control functions.
The safe and efficient operation of fluid power systems, system components, and related equipment requires a means of controlling pressure. There are many types of automatic pressure control valves. Some of these automatic pressure control valves merely provide an escape for pressure that exceeds a set pressure; some only reduce the pressure to a lower pressure system or subsystem; and some keep the pressure in a system within a required range.
Some fluid power systems, even when operating normally, may temporarily develop excessive pressure; for example, when an unusually strong work resistance is encountered. Relief valves are used to control this excess pressure. Relief valves are automatic valves used on system lines and equipment to prevent over pressurization. Most relief valves simply lift (open) at a preset pressure and reset (shut) when the pressure drops slightly below the lifting pressure. They do not maintain flow or pressure at a given amount, but prevent pressure from rising above a specific level when the system is temporarily overloaded.
Hydrostatic vehicle propulsion systems frequently are configured only for two motor propel hydraulic circuits and are not directed to four motor propel hydraulic circuits. The provision of a hydrostatic vehicle propulsion system configured only for two motor propel hydraulic circuits, limits the traction control of these systems as the remaining tires are not propelled and thus have reduced traction capabilities.
Those hydrostatic vehicle propulsion systems configured for four motor propel hydraulic circuits frequently suffer from reduced tractive effort, wheel slippage, and tire scuffing problems. These problems arise as these hydrostatic vehicle propulsion systems configured for four motor propel hydraulic circuits frequently have insufficient circuit design to provide proper traction. Further, these four motor propel hydraulic circuits frequently have very complex valving structures for the control of fluid pressure in the circuits. These complex valving structures add complexity to the systems, which decreases reliability and increases manufacturing and maintenance costs.
It is a primary objective of this invention to provide a hydrostatic vehicle propulsion system consisting of a single, variable fluid displacement pump in conjunction with multiple fluid displacement motors, and a valve system to provide improved traction control functions.
These and other objects will be apparent to those skilled in the art.